In recent years, hearing-aid systems mainly including hearing aids have been remarkably developed, and various kinds of value-added products are about to be on the market.
A well-known problem that occurs when a user of a hearing aid listens to sound from an AV apparatus or the like represented by a television set is that the user has difficulty in listening to the sound from the AV apparatus due to various factors such as surrounding sounds amplified together with the desired sound by the hearing aid.
In order to facilitate listening to desired sound from an AV apparatus, various kinds of systems have been conventionally provided which are intended to transmit, wirelessly or by a radio wave, sounds output from an AV apparatus or the like to a hearing aid. For example, PTL (Patent Literature) 1 and PTL (Patent Literature) 2 disclose a radio wave relay transmission technique of transmitting sounds to a hearing aid using analog FM electric wave and magnetic field induction, taking a specific example of an AV apparatus or the like intended for guidance announcement in a public space. Furthermore, PTL (Patent Literature) 3 discloses, as a technique similar to the above technique, a radio wave relay transmission technique obtained by combining a short-distance digital radio communication in the Bluetooth standard and magnetic field induction communication. According to this technique, it is possible to easily transmit, by a radio wave, audio signals from an AV apparatus to a hearing aid by connecting a radio wave adaptor or the like that supports the BlueTooth standard to the AV apparatus.